PHYSICS FULL (Modules 5-8)

Law of Universal Gravitation

F = Gm₁m₂ / d²

range

the horizontal displacement of an object from its launching point

trajectory

the path of a projectile

terminal velocity

constant velocity attained for a falling object

• drag force is equal and opposite to weight force → F_net = 0

air resistance (drag)

air particles that apply a friction force on the projectile

projectile

an object that is projected into the air, but not propelled as in a rocket

centripetal force

the force that keeps an object moving in a circle, pointing straight toward the center of the path

circular motion (in a magnetic field)

created when a net force supplied by the interaction of the charged particle with the magnetic field IS the centripetal force

tension

a pulling force acting through a medium such as a rope or chain

banked (curve)

making the corner angled with respect to the ground

angular velocity (curly w)

measured in radians/second

stroboscopic image

a photograph that captures multiple sequential phases of a moving subject within a single frame (e.g. at 100Hz frequency)

kinetic energy

the energy associated with motion

potential energy

energy associated with it due to its position relative to another object or within a field

mechanical energy (E_m)

the sum of potential and kinetic energy

Principle of Conservation of Mechanical Energy

If in a system of bodies, there are no other forms of energy except kinetic and potential energy, then the total mechanical energy of the system is constant, ie. (E_m)_initial = (E_m)_final

torque

rotational effect that a force has on an object

satellite

any object that is orbiting the Earth, Sun or other massive body

orbital radius

= radius of central body + altitude of satellite

Kepler’s First Law (the law of ellipses)

Each planet moves, not in a circle, but in an ellipse, with the sun, off centre, at focus.

Kepler’s Second Law (the law of equal areas)

As the planet travels around the orbit, the area covered by a line joining the sun to the planet sweeps out equal area in equal times

Kelper’s Third Law (the law of periods)

For all planets, the cube of the average radius is proportional to the square of the orbital period; that is, r³/T² is constant for all planets going around the sun

Van Allen belts

two invisible, donut-shaped rings of high-energy charged particles—specifically protons and electrons—trapped by Earth's magnetic field

geostationary satellites

an Earth-orbiting satellite that matches Earth's rotation speed, stays positioned directly above the equator, and appears fixed motionless in the sky

theory

a set of concepts, claims and/or laws that can be used to explain and predict a wide range of related observed phenomena. Theories are typically founded on clearly identified assumptions, are testable, produce reproducible results and have explanatory power

law

a statement describing invariable relationships between phenomena in specified conditions, frequently expressed mathematically

field

a region in which a body experiences a force due to the effects of another body. The effect can be the mass within bodies, their charges or magnetic properties

(luminiferous) “aether”

theory that proposed a hypothetical invisible medium permeating all of space through which light waves traveled (as there was a need back then for a medium in which these waves travelled through)

electromagnetic spectrum

the complete range of electromagnetic waves

classical physics

physics as it was understood before the advent of quantum physics and relativity. The term is generally applied to the rules of physics that were establiished before the end of the 19th century

quantum theory

which treates light not as an electromagnetic wave but as a stream of photons or an excitation in what is known as the quantum field.

optical density

the wave can be delayed depending on the features of a medium (e.g. distance between atoms, properties of atoms in the medium) this is quantified by the refractive index

refractive index

the more optically dense the medium, the greater the delay in the journey that light takes through the medium

Snell’s Law

n₁sinθ₁ = n₂sinθ₂

Corpuscular or Particle theory of light

put forward by Newton - stated that light consisted of small particles

Wave theory of light

put forward by Huygens - stated that light consister of waves. He proposed that every point on a wavefront is a source of circular wavelets that spread out in the forward direction in the same speed as the wave itself → constructively and destructively interfere to create new wavefronts

diffraction

occurs when waves bend around small obstacles, or when waves spread out after they pass through small openings

diffraction patterns

these occur because each point on the wavefront moving through the slit acts like a point source (Huygen’s model)

Young’s double slit experiment

aim: to test whether light behaves as a particle or a wave, he shone light through two narrow slits onto a screen, and the resulting pattern of alternating bright and dark bands proved that light travels as a wave.

Law of superposition

when two or more waves overlap in space, the total displacement at any point is the algebraic sum of the individual displacements of each wave (they can constructively and destructively interfere

polarisation

the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave

“unpolarised” light"

composed of many waves with all possible directions of polarisation

Malus’ Law

I = I_maxcos²θ

ideal polarising filter

____ will remove all but the electric fields that are parallel to the axis of the filter

Thomas Kuhn’s technique of analysising a scientific theory

• accuracy: Do observations match the prediction of the model?

• simplicity: is the model simple to understand? Do some explanations begin to get complicated (e.g. Newton’s explanation of diffraction)?

• explanatory power: How much does each model explain? Are there any contradications within the model?

Poisson’s spot

a phenomenon supporting Huygen’s wave model. It is the diffraction pattern produced by a small spherical object in the path of parallel light rays

black body

an imaginary object that perfectly absorbs radiation (and also a perfect emitter) at all wavelengths

black body radiation

thermal electromagnetic radiation emitted by an idealized, perfectly opaque, and non-reflective body in thermodynamic equilibrium

Wein’s Displacement Law

states that the wavelength distribution of thermal energy froma black body at any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph (slid across) → as temp increases the peak wavelength moves towards lower wavelengths

photoelectric effect

the process in which a photon ejects an electron from an atom so that all the kinetic energy of the photon is absorbed in separating the electron imparting kinetic energy to it

kinetic energy

the energy that an object posesses by virtue of its motion

stopping voltage

(polarity of the system is reversed) voltage for each metal to stop the photoelectric current (ie the voltage from battery opposes the current created by the ejected electrons from the photoelectric effect → net zero current therefore can calculate the amount of electrons

work function (Φ)

the minimum energy needed to emit photoelectrons (photoelectric effect)

threshold energy (h)

aka. the work function

frame of reference

a coordinate system that enables the position of a body to be specified

interial frame of reference

a reference frame in which a body moves at a constant velocity unless acted on by a net force

the Galilean principle of relativity

states that there is no absolute frame of reference — no intertial frame of reference is the preferred frame of reference and all velocities are relative

Michelson-Morley experiment

that showed light travels at the same speed in all directions, proving the "luminiferous aether" does not exist

Einstein’s postulates of special relativity

1. The speed of light in a vaccum is an absolute constant

2. All inertial frames of reference are equivalent

Simultaneity

All intertial frames of reference are equivalent (all motion is relative - this means that no two events can be simultaneous in all diffferent frames of reference)

time dilation

time in a moving frame of reference always passes more slowly when observed from any other frame of reference

length contraction

an object moving fast looks shorter in the direction it travels (when viewing from an external frame of reference)

atomic clocks

an extremely precise timekeeping device that measures time by 1 second is the amount of time it takes a caesium-133 atom (in a precisely defined state) to oscillate 9,192,631,770 times by monitoring the resonant frequency of atoms

rest mass (invariant mass)

the mass measured in the frame of the body

relativistic momentum

the momentum of an object moving at a speed close to the speed of light, calculated by multiplying classical momentum by the Lorentz factor

Positron Emission Tomography (PET)

a gamma imaging technique that uses radiotracers that emit positrons (e⁺), which are the antimatter counterparts of electrons

radiotracer

a chemical compound in which one or more atoms have been replaced by a radioisotope (e.g. fluroine-18 to make radioactive glucose, which is preferentially taken up by brain and cancer cells)

field

a region in which a body experiences a force due to the effects of another body. The effect can be the mass within the bodies, their charges or magnetic properties

work-energy theorem

the work done on a system is equal to its change in kinetic energy

the net work done by all forces acting on an object is equal to the change in its kinetic energy (if you do work on an object, it will change its energy)

Law of Conservation of Energy

In a closed system when energy is transformed from one form to another, the total amount of energy remains the same

work

displacement of an object moved parallel to a field

emf (electromotive force)

aka. voltage

the amount of energy that the battery gives to each coulomb of charge

electron volt

One electron volt (1eV) is the amount of energy gained (or lost) by the charge of a single electron moving across an electrical potential difference of one volt

magnetic field

a 3D region of space where a magnetic dipole will experience a force

magnetic flux (Φ - phi)

measured in Wb (weber) is a measure of the amount of magnetic field permeating a space

motor effect

where a current-carrying conductor (such as a wire) placed in an external magnetic field experiences a force

aka. Lorentz force

magnetic flux density (B)

the degree of concentration of flux

area vector (A)

a vector perpendicular to the plane of the area of the object in the field

flux linkage

is the total magnetic field lines passing through a multi-turn coil, calculated by multiplying the number of turns (N) in the coil by the magnetic flux (Φ)

galvanometer

a sensitive ammeter that allows measurement of current in two directions with a zero reading at the centre of the dial

Lenz’s Law

“the direction of the current induced in a conductor by a changing magnetic flux is such that the magnetic field created by the induced current opposes the initial changing magnetic flux.”

permeability (μ)

the measure of ease, with which mangetic lines of force pass through a given material — how easy it is for flux lines to pass through it

primary coil

the input coil which has an AC current running into it

secondary coil

the output coil

eddy currents

circular currents set up in the metal object near where the change in flux is occurring

produced in solid sheets or blocks of conductors (metals) and are produced at right angles to the direction of the changing flux → causes transformers to not be 100% efficient as the creation of these currents uses energy

torque

the turning moment of a force

motors

change electrical energy into mechanical, kinetic or potential energy

split-ring commutator

acts as a switching device to change the direction of the current in the coil every half rotation (uses DC)

armature

component of DC motor

the rotating core that converts electrical energy into mechanical energy

rotor coil(s)

component of DC motor

insulated copper wire wrapped around an iron core. When energized, these coils create an electromagnet that interacts with stationary magnets (the stator) to generate rotational force (torque)

brushes

component of DC motor

conductive components (usually made of carbon and copper) that transfer electrical current from the stationary power source to the spinning rotor (armature) through the commutator

axle

component of DC motor

an electric motor that connects directly to, or integrates with, a drive axle to turn wheels or mechanical parts

back emf (curly E)

The emf induced in opposition to the supply emf running the motor

AC generator

a device which converts mechanical energy into electrical energy → outputs power in the form of alternating voltage and current

slip ring commutator

an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires rotation while transmitting power or signals.

USED IN AC MOTORS/GENERATORS

DC generator

can be made from an AC generator by using a split-ring commutator rather than slip rings

can be made by using a bridge rectifier circuit which converts the AC output from the generator into DC output

turning mechanism

allow method/means to mechanically rotate the coil (in a generator)

stator windings

the electrical coils housed inside a stator (the stationary part of a rotary machine) → in an AC generator

AC induction motor advantages (over other types of motor)

• simple design (simple and cheap to construct)

• reliability - no brushes or commutators, little friction to wear parts down (which would need to be replaced over time)

• can be built to suit almost any industrial requirement

• are economical and efficient to run (for most purposes)

• polyphase induction motors are self-starting → when you turn AC source on, the motor starts (doesn’t require special starting means)

single-phase generator

produces electrical power using a single, continuously alternating voltage